Method And Apparatus For Closure Of An Earth Borehole

ABSTRACT

A method and an apparatus for closing an earth borehole, wherein an expandable closure body is inserted into the earth borehole and expanded in its diameter in order to seal the leak. The closure body, at least a part thereof, is moved beyond the lower end of the borehole to enter into the raw material filled cavity, and is expanded within the cavity below the borehole and, with an axially sealing surface, is urged from below against the cavity&#39;s sealing surrounding the borehole. With regard to the device, to achieve this, the expandable part has an expandable portion with an axially sealing surface which, once expanded, has a diameter significantly greater than the diameter of the borehole. In order to permit the sealing part being pushed against the borehole wall once it has been expanded inside the cavity, a reversible feed motion or advancing drive is provided.

BENEFIT CLAIMS

This application is a US National Stage of International Application No. PCT/EP2011/005459, filed 28 Oct. 2011, which claims the benefit of DE 102010050368.1, filed 3 Nov. 2010. Each application is hereby incorporated in its entirety as if fully set forth herein.

FIELD OF INVENTION

This invention concerns a method and an apparatus for closing an earth borehole, wherein an expandable closure body is inserted into the earth borehole and expanded in its diameter in order to seal the leak.

BACKGROUND OF THE INVENTION

Subterranean raw materials such as oilfields and gas springs are usually reached via boreholes, which are drilled vertically or diagonally through the various layers of earth before reaching the raw materials. Such boreholes can thereby be inserted from the surface, deep into the ground or to the bottom of the sea.

In order to prevent any raw materials escaping through the borehole, especially when they are under high pressure, a ‘Blowout-Preventer’ is usually installed at the top end of any borehole (or a continuing piece of piping originating from it), with which the borehole can be closed off. To do this, a valve mechanism is in place within the Blowout-Preventer that will only be open if set to do so specifically but will otherwise automatically close. Problems arise, if this closure mechanism fails as a result of damage or any leaks are present between the blowout preventer and the borehole near the junction of the borehole at the surface. In order to prevent the uncontrolled leak of, for example oil, it has been suggested to cover the area surrounding the leak on the borehole at the bottom of the sea or ground with sufficient material such as sand and/or a sand-concrete mix in order to thereby achieve closure of the leak. Depending on the surrounding environment and the pressure of the leaking raw material, this method has however been demonstrated to be unreliable and quite slow to carry out, as any raw material under sufficient pressure will be leaking in between the ground surface and the covering material before it has a chance to settle/harden onto the ground.

Hence, it has been suggested to close boreholes by insertion of expandable closing device which when inserted through the borehole in a folded/collapsed fashion, can then be expanded radially, so that the circumference of the expandable part will then be pressing against the inside walls of the borehole. Such radially expanding devices are previously known from DE 20 2009 010 814 U1, EP 0 842 348 B1, or DE 39 21 189 A1. The radial expansion of the insulating part is achieved here for example via a clamping mechanism where, through axial adjustments, an elastic clamping ring will be pushed outwards or for example by axial pushing of rubber bands between two bars, the axially squeezed rubber bands will be pushed radially.

The complete insulation of leaks with such radially expansive closing devices in a borehole is however very difficult in soft layers of earth or irregular boreholes. Furthermore, the expandable parts of these closing devices are also limited to a degree, so that following the give of the borehole, a sufficient pressure and seal can no longer be achieved. A similar situation arises in the situation of irregularly formed boreholes, where a stream of raw material may bypass the expandable part. This could in a way be avoided by having a sufficiently soft expandable part that could mold itself sufficiently to the contour of the borehole. On the other hand, the expandable part must be of a sufficiently hard material to withstand the pressure from the cavity holding the raw material in order to prevent the device from being expelled upwards towards the surface.

SUMMARY OF THE INVENTION

The objective underlying the present invention is to provide for an improved process as well as an improved apparatus, in order to avoid the above explained problems and to further develop the process and apparatus in an advantageous manner. Preferably, it should be possible to close any leaking borehole even if its walls are irregular or with poor ground substance and without having to require long preparation times and complex machinery.

According to the present invention this objective is achieved by a method for closing an earth borehole, wherein an expandable closure body is introduced into the borehole and is expanded in its circumference to close the borehole, characterized in that at least part of the closure body is moved out of the lower end the borehole, and expanded within earth cavity, and, with an axially sealing surface, it is urged from below against the ceiling of the cavity surrounding the borehole.

Additionally, the present invention is an apparatus for closing and sealing an earth borehole, comprising an expandable closing device that, in the collapsed state, has a smaller diameter than the borehole, characterized in that said closing device is provided with an axially sealing surface at an expandable sealing portion, whose diameter in the expanded state, is bigger than the borehole circumference, and a reversible feeding drive is provided for moving the closing device forwardly beyond the end of the earth borehole into the cavity below the borehole, and for moving the closing device backwards with the axial sealing surface being urged against the ceiling surrounding the borehole after expansion of said sealing portion.

It is suggested to seal the borehole from its inferior end, where the borehole ends into the raw material filled cavity, in order to use the pressure exhibited by the raw material to press the expandable part of the device against the ceiling surrounding the inferior end of the borehole, thereby achieving a seal. According to the present invention, the closure body, at least a part thereof, is moved beyond the lower end of the borehole to enter into the raw material filled cavity, and is expanded within the cavity below the borehole and, with an axially sealing surface, is urged from below against the cavity's sealing surrounding the borehole. With regard to the device, to achieve this, the expandable part has an expandable portion with an axially sealing surface which, once expanded, has a diameter significantly greater than the diameter of the borehole. In order to permit the sealing part being pushed against the borehole wall once it has been expanded inside the cavity, a reversible feed motion or advancing drive is provided. This drive allows the end of the device first being inserted into the cavity to allow the device to expand, before retracting it so that the expanded device sits tightly against the borehole thereby sealing it off. As the borehole is now sealed from its inferior end, both erosions within the borehole wall or axial fixation issues are no longer an issue. Additionally, the seal will be enforced by increasing pressures within the cavity, as it is this pressure exhibited by the liquid or gas within the cavity which will press the device against the borehole thereby sealing it off. This sealing pressure against the ceiling of the cavity surrounding the borehole, will essentially be running parallel to the longitudinal axis of the borehole.

Our device will not be expanded in enlarged areas within the borehole but instead it will be driven all the way into the cavity containing the liquid or gaseous raw materials to be accessed. It will then be expanded and reversed against the ceiling of the cavity sealing off the borehole. The ceilings of such cavities tend to be quite even and according to its slope, will be close to perpendicular to the borehole. Depending on the environmental circumstances, those parts of the cavity are usually drilled into, where the angle of the borehole to the cavity ceiling will be between 70-100 degrees but preferably 80-100 degrees or in perfect conditions, 90 +/−5 degrees. This means that the borehole will be nearly perpendicular to the ceiling of the raw material containing cavity, which is an advantage for our device, which can hence exhibit its maximal axial sealing ability.

The sealing of the borehole is hence exclusively achieved by axial (i.e. in the direction of the borehole) pressure pushing our closing device's expandable part against the cavity ceiling. This is achieved by the retraction of the closing device pulling the expandable part backwards towards the borehole as well as the pressure exhibited by the raw material pushing it against the ceiling surrounding the borehole. When expanded, the closing device will have a sufficiently big axial pressure impingement area, which will be facing away from the cavity ceiling. This impingement area will be running close to parallel to the cavity ceiling and/or have an even surface so that the pressure exhibited by the raw material will exhibit a mainly axial force onto our closing device. The impingement area is sufficiently big and constructed in a way that it will be using the pressure exhibited by the raw material to push the sealing area of the closing device sufficiently tight against the ceiling of the cavity.

The previously mentioned expandable sealing part of the closing device can essentially be constructed and be expanded in several ways. This can be a collapsible, hinged or folding umbrella—like element, whose surrounding margins will be the sealing area. With such a hinged, unfolding umbrella element, a sealing surface area much bigger than the borehole will be achieved. As a result, the risk of further leaks is much smaller as it will be unlikely to be affected by erosions surrounding the borehole. Secondly, a big surface impingement area is achieved against which the raw material will be pushing—this will push the sealing device closely against the cavity ceiling.

Furthermore, the closing device and/or its expandable sealing part are constructed as such, that the axial sealing surface (under the pressure of the raw material) will be locked into the ceiling, scraping or digging in a little. The expandable sealing part can be constructed so that, after expansion of a margin piece, this will be pushed against the ceiling. As further pressure is exhibited against the more central area, the device will widen against the direction of its introduction. As the central area is pressed on, the axial sealing area will be expanded further along its margins, so that the axial sealing area is essentially scraping or digging into the ceiling. The pressure within the cavity will exhibit the pressure against the central area. Hence, the device can be made of material sufficiently elastic and or moldable so that it can adjust its shape perfectly according to the shape of the ceiling.

The expandable part can be shell-like, dome or cone shaped, so that, in the expanded state of the sealing part, the margins will be in touch with the ceiling whilst the central part of the device will be furthest away from the borehole. For example, the device could be in the shape of an umbrella, where each flank has a narrow angle of 10-35 degrees. This could then form the covering surface, perpendicular to the borehole and the rest of the device.

The umbrella like part will be expanded from the side facing the borehole creating a shallow concave covering surface. The umbrella like part will then be pushed against the ceiling from below (i.e. from within the cavity), this will result in further expansion of the umbrella like part so that the margin's axial sealing area will be locked into the ceiling. This digging in mechanism leads to a particularly effective seal. The pressure below, exhibited by the raw material will hence be working to expand the device further whilst locking/digging it into the ceiling.

Following a further progress of the invention, the expandable sealing part of the closing device may also contain a fluid filled balloon ring with a collapsible cover into which for example oil or gas could be filled. To insert the closing device into the borehole, the balloon will be ‘deflated’ so that its diameter is smaller than the borehole. Once the cavity underneath the borehole is reached, the pressure fluid will be injected into the cover of the balloon in order to inflate it. Once ‘inflated’, the balloon ring will be bigger than the borehole diameter. The balloon ring will then be pressed against the ceiling by the pressure within the cavity, thereby achieving an effective seal.

After further development of the invention, the expandable sealing part may also have different expansion mechanisms.

The sealing part of the closing device and/or the within contained axial sealing surface has an outer diameter of at least 150% and preferably 200% of the borehole diameter. This will ensure that any erosion surrounding the borehole will be sufficiently covered and high sealing pressures can be achieved.

The previously named axial sealing area can have the shape of a ring as long as the inside diameter of the ring is still substantially larger than the borehole diameter. Ideally, the width of the ring is relatively narrow so that high area pressures can be achieved against the cavity ceiling. If the outer diameter is 150% of the borehole, the inner diameter should be more than 125%, vice versa, if the outer diameter is more than 200%, the inner diameter should be 150% or more.

The closing device can generally be inserted into the borehole in different ways and be positioned from within the cavity to cover the borehole opening. The closing device can be inserted into the borehole together with a drill head on a boring bar. The drill head, being introduced in front of the closing device, can then be left within the cavity when the closing device is in place. Although, the drill head may in fact be joined onto the closing device or if need be, get disconnected and then dropped into the cavity.

Alternatively or additionally, the closing device can also be brought into the borehole on a self-driving vehicle. This vehicle may take the form of a cartridge or an escalator basket for example. This vehicle can transport the closing device through the borehole, until at least part of the closing device is placed within the cavity. After expansion of the device, the vehicle, which is still within the borehole, will then be reversed backwards, thereby pulling the axial sealing surface closely against the cavity ceiling.

The closing device can also contain a valve, which, even if the closing device is securely in place, allows liquid or gaseous raw material to be extracted through the borehole. This can be finely adjusted and will be used to help prevent dangerously high pressures building up within the cavity. When the valve is closed, any raw material leaks will be prevented and seals the cavity off completely from the borehole. Such a valve could also be installed prior to any problems arising, such as when the borehole is first put in place. During the controlled extraction of the raw material the valve will be open. As soon as problems arise, the valve will be shut close, so that no further raw materials can leak out. Preferably, this mechanism will be set so that, the valve is closed in its neutral state and will only open if specifically switched to do so. If this switch is not working, the valve would automatically be in its neutral closed state.

These and other objects, features and advantages of the present invention will become more apparent upon reading the following specification in conjunction with the accompanying drawing figures.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will now be explained in further detail. Several embodiments are illustrated by the drawings which show:

FIG. 1: a schematic drawing demonstrating the apparatus to close a borehole. In this version, the device is lowered from a ship into a borehole located on the bottom of the sea.

FIG. 2: a partly enlarged view of the closing device in FIG. 1. Shown as the device is still in the borehole above the raw material containing cavity.

FIG. 3: a partially enlarged view of the closing device. Shown once located within the raw material containing cavity but not expanded.

FIG. 4: a partially enlarged view of the closing device. Shown in a similar position to FIG. 3. Here, the expandable part is expanded but not yet in close contact with the ceiling of the cavity.

FIG. 5: a partially enlarged view of the closing device. Here the device is fully expanded and fully pressed against the cavity ceiling thereby sealing the borehole off.

FIG. 6: a partially enlarged view of the closing device. Similar to FIG. 4, although one can see the drill head in place on this schematic drawing.

FIG. 7: a partially enlarged view of a further version of the closing device. Here one can visualize the self driving vehicle and a different version of the closing device: the expandable part of this device is achieved by filling off a balloon.

DETAILED DESCRIPTION OF EMBODIMENTS

To facilitate an understanding of the principles and features of the various embodiments of the invention, various illustrative embodiments are explained below. Although exemplary embodiments of the invention are explained in detail, it is to be understood that other embodiments are contemplated. Accordingly, it is not intended that the invention is limited in its scope to the details of construction and arrangement of components set forth in the following description or illustrated in the drawings. The invention is capable of other embodiments and of being practiced or carried out in various ways. Also, in describing the exemplary embodiments, specific terminology will be resorted to for the sake of clarity.

It must also be noted that, as used in the specification and the appended claims, the singular forms “a,” “an” and “the” include plural references unless the context clearly dictates otherwise. For example, reference to a component is intended also to include composition of a plurality of components. References to a composition containing “a” constituent is intended to include other constituents in addition to the one named.

Also, in describing the exemplary embodiments, terminology will be resorted to for the sake of clarity. It is intended that each term contemplates its broadest meaning as understood by those skilled in the art and includes all technical equivalents which operate in a similar manner to accomplish a similar purpose.

Ranges may be expressed herein as from “about” or “approximately” or “substantially” one particular value and/or to “about” or “approximately” or “substantially” another particular value. When such a range is expressed, other exemplary embodiments include from the one particular value and/or to the other particular value.

Similarly, as used herein, “substantially free” of something, or “substantially pure”, and like characterizations, can include both being “at least substantially free” of something, or “at least substantially pure”, and being “completely free” of something, or “completely pure”.

By “comprising” or “containing” or “including” is meant that at least the named compound, element, particle, or method step is present in the composition or article or method, but does not exclude the presence of other compounds, materials, particles, method steps, even if the other such compounds, material, particles, method steps have the same function as what is named.

It is also to be understood that the mention of one or more method steps does not preclude the presence of additional method steps or intervening method steps between those steps expressly identified. Similarly, it is also to be understood that the mention of one or more components in a composition does not preclude the presence of additional components than those expressly identified.

The materials described as making up the various elements of the invention are intended to be illustrative and not restrictive. Many suitable materials that would perform the same or a similar function as the materials described herein are intended to be embraced within the scope of the invention. Such other materials not described herein can include, but are not limited to, for example, materials that are developed after the time of the development of the invention.

FIG. 1 shows a borehole 1, the bottom of the sea 2 with a raw material containing cavity 3.

Via a platform 4 on the sea surface, such as a ship, apparatus 5 can be inserted into borehole 1 in order to seal off the latter.

Apparatus 5, contains as demonstrated in more detail in FIGS. 2 to 5, the closing device 6, which can be inserted via boring bar 7 or a similarly suited device, from above into the borehole 1. If a platform 4 is used in combination with a boring bar 7, this can be powered by the forward feed apparatus 8.

In FIG. 2, the apparatus is shown whilst still positioned in the borehole. The closing device is in its collapsed state so that the outer circumference of the closing device is smaller than the borehole circumference.

As shown in FIG. 3, the closing device 6 is inserted through the inferior end of the borehole 1 into the cavity 3, so that the entire expandable sealing part 9 is outside borehole 1 and inside cavity 3. Once this position is established, the sealing part 9 can be radially expanded until its outer diameter D is substantially bigger than the diameter d of borehole 1. See also FIG. 4 and FIG. 5.

In the schematic drawings FIGS. 2 to 5, the sealing part 9 is composed of a foldable umbrella element 10, which similar to the construction of a basic umbrella consists of multiple supporting breams covered by a membrane. From these breams, further foldable axis will be able to unfold in order for the umbrella membrane to unfold as shown in the figure. This membrane is made of a sufficiently stable, moldable material such as a highly resistible laminate or foil material such as in the form of several layers of aramid fiber laminate.

In order to expand the sealing part 9, the expansion power unit 11 is in place, which in this figure's construction, could for example be in place for the umbrella element 10 at the closing device 6.

Once the sealing part 9 is sufficiently widened, the closing device 6 will be reversed by the forward feeding apparatus pulling back against the direction of insertion, until the axial sealing surface 13 of the sealing part 9 is pressed against the ceiling 12 of the cavity 3.

The axial sealing surface 13 is a circular surface conveniently placed at the outer margin of the sealing part 9 and it is on the backward orientated contour of the sealing part 9. In other words, the axial sealing surface 13 is placed at that part of the sealing part 9, which in the expanded state, is facing the ceiling 12. Please see FIG. 5.

Conveniently, sealing part 9 forms a mildly concave cover once expanded. See FIG. 5. The angle of the contour of sealing part 9 can vary, although shallow shapes would be most beneficial. For example, the sealing part 9 is suited to angles of 2× 5 degrees to 2× 20 degrees, so that a shallow cone is formed as a result. If the sealing part 9 is in its position covering the borehole 1 as shown in FIG. 5, the pressure p generated within the cavity to press down on the centrally elevated sealing part 9 of the closing device 6. Once this is giving in even slightly, the axial sealing surface 13 will be expanded a little further locking itself into the ceiling 12.

As shown in FIG. 6, the closing device 6 can also be introduced together with the drill head 14 into the borehole 1. The drill head will be placed ahead of the closing device and have an at least marginally bigger diameter than the closing device in its non-expanded state. Hence, the closing device 6 can be brought straight through the borehole 1 into the cavity 3 where it can be fixed into place. Here, the drill head 14 can either stay in the cavity 3 and/or be attached to the closing device 6. Otherwise FIG. 6 is similar to the previous ones—please refer to previous explanations for further detail.

FIG. 7 shows a further development as part of this invention: The closing device 6 is now brought through the borehole via a self-driving vehicle 15. The vehicle 15 contains a forward feeding device, which could take the form of wheels 16, which are pressed against the walls of the borehole. Conveniently, forward feeding device is attached to the vehicle and can be driven by an engine whose energy can be supplied from the water surface or ground level. Furthermore, the expandable sealing part 9 contains a balloon, which in the deflated state has a smaller diameter than the borehole and can hence be easily introduced. Once within the cavity, the balloon 17 can then be filled with fluid or gas so that its diameter will now be bigger than the borehole 1. The balloon 17 is shown to be ring shaped in the below drawing, but could equally be circular or mushroom shaped. The back contour of the balloon 17 forms—in the expandable state—the axial sealing surface 13 which is pushed against the ceiling 12 of the cavity 3. This occurs secondary to the retraction of the forward feeding engine, which will now pull the balloon 17 backwards into the borehole 1. Secondly the pressure within the cavity 3 will push the entire device in the direction towards the ceiling 12, thereby exacerbating the seal. Please see FIG. 7.

Numerous characteristics and advantages have been set forth in the foregoing description, together with details of structure and function. While the invention has been disclosed in several forms, it will be apparent to those skilled in the art that many modifications, additions, and deletions, especially in matters of shape, size, and arrangement of parts, can be made therein without departing from the spirit and scope of the invention and its equivalents as set forth in the following claims. Therefore, other modifications or embodiments as may be suggested by the teachings herein are particularly reserved as they fall within the breadth and scope of the claims here appended. 

1. Method for closing an earth borehole comprising: introducing an expandable closure body into a borehole; and expanding the closure body in its circumference to close the borehole; wherein at least part of the closure body is moved out of the a lower end the borehole, and expanded within an earth cavity, and, with an axially sealing surface, it is urged from below against the a ceiling of the cavity surrounding the borehole.
 2. Method according to claim 1, wherein an expanding body is used, which, after expansion, is set, with an edge portion, onto the cavity's ceiling, and is splayed and spread out by retracting the expanding body towards the borehole in the direction opposite to the inserting direction.
 3. Method according to claim 1, wherein the closure body, together with a drill head, is inserted into the borehole via a boring bar, wherein the drilling head is positioned ahead of the closure body when considering the direction of insertion and is left in the cavity also after having closed the borehole.
 4. Method according to claim 1, wherein the closure body is transported through the borehole via a self-propelling vehicle which, after expansion of the closure body, is reversed back in the borehole until the closure body's axially sealing surface is in contact with the ceiling of the cavity.
 5. Method according to claim 1, wherein the cavity is a cavity containing liquid or gaseous crude materials and whose ceiling is approximately perpendicular to the direction of the borehole, wherein an axial sealing surface of the closing body is also approximately perpendicular to the direction of the borehole, wherein the closing device and the axial sealing surface are moved against the cavity's ceiling axially in the direction of the longitudinal axis of the earth borehole.
 6. Method according to claim 1, wherein the sealing of the borehole is achieved exclusively by axial pressure of an axial sealing surface against the ceiling in the direction of the longitudinal axis of the borehole, wherein the axially sealing surface is pressed against the cavity's ceiling by pressures exhibited by gas or fluid from within the cavity.
 7. Method according to claim 1, wherein the closing body contains an expandable umbrella element at whose outer margin an axial sealing surface is located, which umbrella element is expanded in the cavity below the borehole in such a fashion, that the closing body forms a concave dome towards the borehole, which dome shaped expanded umbrella is flattened and further expanded, locking or grabbing itself into the ceiling, as the pressure of the fluid or gas within the cavity is pushing against it back towards the borehole.
 8. Apparatus for closing and sealing an earth borehole comprising: an expandable closing device that, in the collapsed state, has a smaller diameter than a borehole, wherein the closing device is provided with an axially sealing surface at an expandable sealing portion, whose diameter in the expanded state, is bigger than the borehole circumference, and a reversible feeding drive is provided for moving the closing device forwardly beyond the end of the earth borehole into a cavity below the borehole, and for moving the closing device backwards with the axial sealing surface being urged against a ceiling surrounding the borehole after expansion of said sealing portion.
 9. Apparatus according to claim 8, wherein the expandable sealing portion has a swinging or unfoldable umbrella element at whose outer margin the axial sealing surface is contained.
 10. Apparatus according to claim 8, wherein an expandable sealing part's roof which is facing the ceiling of the cavity, forms a concave, expansion or spreading body, whose outer margin forms the axial sealing surface.
 11. Apparatus according to claim 8, wherein the expansion or spreadable body is adapted to be deformable, such that said expansion or spreadable body is able to be flattened by the pressure exhibited by the fluid/gas within the cavity and as a result expand the axial sealing surface radially.
 12. Apparatus according to claim 8, wherein the expandable sealing part, in the expanded state, has a diameter of at least 150%, of the borehole diameter.
 13. Apparatus according to claim 8, wherein the axial sealing part forms a ring shaped surface, whose inner diameter is bigger than the diameter of the borehole.
 14. Apparatus according to claim 8, wherein the closing device comprises a valve mechanism which is situated in a connection channel, which has an opening towards the borehole as well as to the cavity so, when the valve mechanism is set ‘open’, fluid can stream from the cavity into the borehole.
 15. Apparatus according to claim 8, wherein the closing device in the expanded state, has an approximately planar impingement area extending approximately perpendicular to the longitudinal axis of the earth borehole, wherein the pressure exhibited by the fluid in the cavity acts upon said impingement area which is faced away from the ceiling and contains a surface area of more than 200% of the surface area of the borehole.
 16. Method according to claim 1, wherein the sealing of the borehole is achieved exclusively by axial pressure of an axial sealing surface against the ceiling in the direction of the longitudinal axis of the borehole, wherein the axially sealing surface is pressed against the cavity's ceiling by pressures exhibited by retraction of the closing device back towards the borehole.
 17. Apparatus according to claim 8, wherein an expandable sealing part's roof which is facing the ceiling of the cavity, forms a concave, expansion or spreading body, whose outer margin forms the axial sealing surface, and which expansion or spreading body, within the axially sealing surface, is sloped towards the centre of said closing body.
 18. Apparatus according to claim 8, wherein an expandable sealing part's roof which is facing the ceiling of the cavity, forms a concave, expansion or spreading body, whose outer margin forms the axial sealing surface, and which expansion or spreading body, within the axially sealing surface, is spaced apart from the ceiling of the cavity.
 19. Apparatus according to claim 8, wherein the expandable sealing part, in the expanded state, has a diameter of at least 200% of the borehole diameter.
 20. Apparatus according to claim 8, wherein the axial sealing part forms a ring shaped surface, whose inner diameter is bigger than the diameter of the borehole by at least 180% of the borehole diameter. 